1. Field of the Invention
This invention relates to a solid oxide fuel cell.
2. Related Art Statement
Recently, fuel cells have been noted as useful as power generating equipment. The fuel cell is a device capable of directly converting chemical energy possessed by fuel to electrical energy. Since the fuel cell is free from the limitation of Carnot's cycle, it is an extremely promising technique in that the fuel cell essentially has a high energy conversion efficiency, and various fuels (naphtha, natural gas, methanol, coal reformed gas, heavy oil, etc.) may be used. Moreover, the public nuisance is less, and the power generating efficiency is not influenced by the scale of the equipment.
Particularly, since the solid oxide fuel cell (hereinafter abbreviated as SOFC) operates at a high temperature of 1000.degree. C. or more, the activity of the electrode is very high, and the use of a noble metal catalyst such as expensive platinum is not completely required. In addition, since the SOFC has a low polarization and a relatively high output voltage, the energy conversion efficiency is considerably higher than that in the other fuel cells. Furthermore, since the SOFC is constructed with solid materials, it is stable and has a long use life.
FIG. 6 sectionally shows an example of this type of SOFC.
In FIG. 6, numeral 10 is a supply tube for introducing an oxidizing gas such as air or the like, numeral 6 is a bottomed cylindrical porous support numeral 7 is an air electrode, numeral 8 is a solid electrolyte, numeral 9 is a fuel electrode, numeral 16 is an upper plate supporting the oxidizing gas supply tube 10 and dividing an oxidizing gas chamber 27 and an exhaust gas chamber 17, numeral 20 is a bottom plate supporting an SOFC body 5 and provided with a fuel hole 20a communicating a cell reaction chamber 19 to a fuel chamber 26, numeral 18 is a plate holding an outer periphery of an opening side of the SOFC body 5 and provided with a gas hole 18a communicating the cell reaction chamber 19 to the exhaust gas chamber 17.
When the oxidizing gas such as air or the like is supplied from the oxidizing gas chamber 27 to the oxidizing gas supply tube 10 as shown by an arrow A, it is discharged from an outlet port 10a for the oxidizing gas and turned at the bottomed portion inside the SOFC body 5 as shown by an arrow B to flow out into the exhaust gas chamber 17 as shown by an arrow C. On the other hand, a fuel gas such as H.sub.2, CH.sub.4 or the like is flown through the fuel hole 20a of the bottom plate 20 along an outer surface of the SOFC body 5 as shown by an arrow D. In this way, oxygen inside the SOFC body 5 flows as an oxygen ion through the solid electrolyte 8 to the fuel electrode 9 and reacts with the fuel gas at the fuel electrode 9 to generate a current between the air electrode 7 and the fuel electrode 9, whereby the cell can be used as a fuel cell. Since the fuel cell is used at a high temperature of about 1000.degree. C., the shape of FIG. 6 is capable of being constructed without a seal portion and is said to be preferable because the occurrence of thermal stress can be reduced.
In the SOFC of the above structure, however, the oxidizing gas supply tube 10 and the SOFC body 5 are separately made and the holding of the supply tube 10 is attained only by engaging with the upper plate 16, so that there is caused a problem that the positioning of the supply tube 10 in the SOFC body 5 becomes difficult.
Furthermore, since the position of the supply tube 10 to the SOFC body 5 changes due to the difficulty of the positioning, when the oxidizing gas such as air or the like is supplied through the supply tube 10 and turned at the bottomed portion inside the SOFC body 5 to rise upward between the outer surface of the supply tube 10 and the inner surface of the SOFC body 5, the flowing of the oxidizing gas changes in accordance with the position of the supply tube 10 in the SOFC body 5, so that there is a problem of inconsistent performance among different cells.
Moreover, there is caused a problem that the mechanical strength against vibrations or the like in the mounting or during use are insufficient because the supply tube 10 and the SOFC body 5 are separately made as mentioned above.